A342795 a(n) is the number of core triads with n nodes up to isomorphism and transposition.

1, 3, 9, 24, 62, 159, 381, 927, 2150, 5051, 11483, 26332, 58986, 132796, 294046, 652772, 1431813, 3143879, 6841673

Offset

8,2

Comments

A triad is an orientation of a tree that has a single vertex of degree 3 and otherwise only vertices of degree 2 and 1. A triad T is called a core triad if every endomorphism of T is an automorphism.

Links

Table of n, a(n) for n=8..26.

Example

For n = 9 the a(9) = 3 solutions are:
  1. 0111,000,1
  2. 01000,00,1
  3. 01111,00,1
Here 0 stands for forward edge, 1 stands for backward edge, and the three words stand for the three paths that leave the vertex of degree 3 of the triad.

Crossrefs

Sequence in context: A279978 A269601 A006684 * A267465 A018788 A098690

Adjacent sequences: A342792 A342793 A342794 * A342796 A342797 A342798

Keyword

nonn,more

Author

Michael Wernthaler, Mar 21 2021

Status

approved